Rollover vent valves are widely used and are well known.
For example, U.S. Pat. No. 5,738,132 discloses a roll over vent valve comprising a housing having a fluid inlet and a fluid outlet, the latter comprising a substantially elongated sliT-shaped outlet aperture of the housing bounded by a valve seating. There is furthermore provided a float member located in the housing and axially displaceable within the housing between the inlet and the outlet; an elongated flexible closure membrane strip anchored at one end thereof to an end of the float member adjacent the outlet and at a portion thereof offset with respect to the outlet; spring biassing means located within the housing and bearing on the float member so as to spring bias it in the direction of the outlet; whereby the spring biassing together with buoyancy forces acting on the float member tend to press the membrane strip into sealing engagement with the outlet aperture whilst gravity forces acting on the float member tend to displace the float member away from the outlet so as to progressively detach the strip from sealing engagement with the outlet
US2009071543 discloses a fuel valve comprising a primary valve and a pressure responsive auxiliary valve, both being axially accommodated and displaceable within a common housing formed with a fluid inlet and a fluid outlet port, and a partition extending between the primary valve and the auxiliary valve. The partition comprising a flow passage extending between a primary port at a bottom face of the partition and an auxiliary port at a top face of the partition. The primary port is sealable by a sealing member of the primary valve and the auxiliary port sealable by a sealing member of the auxiliary valve.